An Activated Carbon Filter – Should You Buy?


You’ve probably found that some form of activated carbon filter is offered by many air purifiers if you’ve been looking for an air purifier for any length of time.

On low end products this filter can be a simple foam pre-filter impregnated with a few ounces of activated carbon. On high quality filters you may find a large activated carbon bed of 7 to 160 pounds depending on the model’s residential or commercial use.

Of course you may ask, what is this activated carbon stuff and why should I care? What would I need an activated carbon filter for and if I need an activated carbon filter how do I know what is best? Are those filters with only a few ounces going to benefit me? Should I consider those that offer a large bed of many pounds of activated carbon?

What Is Activated Carbon?

what is an activated carbon

First of all, let’s define what were talking about when we say activated carbon. Carbon comes in many forms. On the one hand its atoms can line up into regular crystalline structures like diamond, graphite, fullerenes and nanotubes. It can also come in an irregular, non-crystalline form referred to as amorphous carbon. We see this most often as soot and charcoal. Soot and charcoal are useless to us as a filter media because they are contaminated with many organic chemical residues left over from the original material the soot or charcoal came from.

Carbon is transformed into activated carbon by treating a raw carbon stock with high temperature steam in the neighborhood of 1000 degrees Celsius in the absence of oxygen. This drives out non-carbon elements and chemical residues and opens up millions of micro-pores that can serve as tiny traps for gaseous chemicals that pass through.

Activated carbon can have from 400 to 1200 square meters of surface area for each gram of material. This huge surface area of microscopic pores and cracks exerts an attractive force known as van der Waals force. This force causes gaseous chemicals passing by to adsorb to the carbon surface and become trapped.

Gases of differing molecular weights may require an activated carbon filter of differing properties. Differing properties from one activated carbon to another are the result of the source of the raw carbon stock, the methods used to create it, and any added chemisorbers and catalysts.

The raw carbon may come from wood, nutshells, coconut husks, animal bones, lignite, coal, or petroleum residues. Various manufacturers will also treat the activated carbon with catalysts and chemisorbers to enhance their ability to adsorb various targeted inorganic pollutants.

This means you may have a wide variety of choices to select from and can find a specific activated carbon filter for your needs.

How Can An Activated Carbon Filter Benefit You?

Most persons looking to buy an air purifier initially do so to relieve an allergy or asthma condition and often think only in terms of particulate irritants like dust, pollen, and dander.

With a little research they begin to realize the substantial negative health effects of the odors and chemicals they are exposed to in their homes and workplaces. It’s because of the ill health effects of chemical contaminants and the need to control them that all better quality air purifiers include an activated carbon filter.

An activated carbon filter can adsorb some of almost any vapor; has a large capacity for organic molecules, especially solvents; adsorbs and retains a wide variety of chemicals at the same time; works well under a wide range of temperatures and humidity levels; is inert and safe to handle and use; and is readily available and affordable. Activated carbon filters are the most effective type of filter against chemicals, gases, cigarette smoke and other odors. They can remove organic acids, alcohols, aldehydes, chlorinated hydrocarbons, esters, ethers, ketones, mercaptans, amines, halogens, halogen acids, sulfuric acid, sulfur dioxide, phosgene, as well as odors from human and animal sources, urine and other waste, perfumes and household cleaning chemicals.

An activated carbon filter can make the air healthier for people in general, but especially asthma sufferers, babies, children, the elderly, and are particularly helpful to people with Multiple Chemical Sensitivity (MCS).

How To Choose The Best Activated Carbon Filter

benefits of air purifiers

For an activated carbon filter to be effective, there needs to be a sufficient amount of activated carbon so that the air passing through the filter is able to deposit its pollutant molecules.

Most air cleaners on the market today include a foam or fibrous pad onto which a few ounces of carbon have been applied. This is so they can claim a broader range of air cleaning capabilities, but in reality such small quantities of carbon are ineffective.

An activated carbon filter needs a deep bed consisting of many pounds of activated carbon to provide sufficient dwell time for the air passing through it to achieve maximum removal of pollutants.

The activated carbon pads found on most filters are also usually part of a pre-filter design that is intended to prevent large particles from prematurely clogging a higher efficiency filter placed behind the pre-filter. Unfortunately this allows fine dust particles to clog the micro pores of the activated carbon and results in very rapid reduction in its effectiveness.

When choosing an activated carbon filter it is important to find one that provides a large bed of many pounds of activated carbon. Additionally the activated carbon media needs to be protected from premature clogging by being placed behind a pre-filter.

An optimal flow of air needs to be available to pass through it. A cylindrical shaped design is an ideal solution for allowing maximum contact with the air.

To capture any carbon dust that may be lost from the activated carbon filter a post filter should be placed after the activated carbon and in front of any other high efficiency filter such as HEPA.

It is best if the air filter’s activated carbon bed and HEPA filter can be replaced separately as the activated carbon filter will typically have a shorter life than the HEPA filter. They both should be relatively easy to access.

Finally, you should be aware that while activated carbon is excellent for removal of highly volatile organic compounds (VOCs), less volatile compounds like formaldehyde and inorganic gases respond best to chemisorbers that break down the pollutants by chemical reaction. Thus, you should look for an activated carbon filter that is impregnated with appropriate media to control the particular pollutants that concern you.

I have found that Allerair air purifiers, with over forty different activated carbon blends available for almost any general application can meet anyone’s needs with ease. Allerair can also provide highly customized blends for special purposes to labs, industry, military or anyone with needs beyond the usual residential, healthcare, or commercial uses.

If you’re going to buy an air purifier, it only makes sense to purchase one that can control practically anything.


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